Weld using gas metal arc welding process (GMAW)

Weld using gas metal arc welding process (GMAW)  GMAW undertaken autonomously or within a team environment using predetermined standards of quality, safety, work and welding procedures and the skills applied to a range of fabrication activities.  A range of material suitable to heavy or light fabrication is used.  Fillet and butt welds in all positions on a range of materials that may include carbon steel or stainless steel, etc.  As a guide, welds produced to the standard of this unit would typically conform to Australian Standard 1554 General purpose, American Bureau of Shipping (ABS) or equivalent.  Preparation of materials may include preheating, setting up of jigs, fixtures, clamps, etc.  Remedial action using thermal processes may include oxyacetylene and air arc equipment.  Grinding devices may also be used.  Where thermal processes, hand andor power tools are required the appropriate specialisation units should be accessed.

5.17A Weld using gas metal arc welding process (GMAW)

Reproduced with the kind permission of the Australasian Welding Journal

Pre-requisites:

5.50A Perform routine gas metal arc welding

18.1A Use hand tools 18.2A Use power tools/hand held operations

5.17A Weld using gas metal arc welding process (GMAW)

Range statement

environment using predetermined standards of

quality, safety, work and welding procedures and

the skills applied to a range of fabrication activities.

fabrication is used

materials that may include carbon steel or stainless

steel, etc.

unit would typically conform to Australian Standard

1554 General purpose, American Bureau of

Shipping (ABS) or equivalent.

setting up of jigs, fixtures, clamps, etc.

5.17A Weld using gas metal arc welding process (GMAW)

Range statement

include oxyacetylene and air arc equipment

tools are required the appropriate specialisation

units should be accessed.

Element 5.17A.1 Prepare materials for gas metal arc

1.2 Material is correctly prepared In this presentation we will look at:

 weld positions and weld types

 methods of plate preparation.

1.3 Materials assembled/aligned to specification where required In this

presentation we will look at:

 material holding devices.

5.17A Weld using gas metal arc welding process (GMAW)

Protective clothing

 Helmet shade 10 - 13 filter lens.

 Flame proof clothing (woollen or cotton):

5.17A Weld using gas metal arc welding process (GMAW)

Hazards in welding

 All welding is hazardous to your own safety and others.

 Electric shock (low voltage, secondary side):

 caused by:

 wet floors and weather.

 Electric shock (high voltage, primary side):

 250 - 415 volts

 caused by:

 tampering with mains power lead

 interfering with internal parts.

 Remedy

 maintain machine by licensed electricians.

5.17A Weld using gas metal arc welding process (GMAW)

General rules

 Wear dry insulated boots.

 Wear dry gloves.

 Work on dry floors.

 Don’t change electrodes with bare hands.

 Don’t cool electrode holders in water.

 Don’t hold electrode under arms.

 Don’t form a circuit.

 In case of electrocution turn off power If unable

remove victim with non-conducting materials

eg: welding leads, wood, dry clothing.

5.17A Weld using gas metal arc welding process (GMAW)

 paint and solvents

 composition of parent metal

 electrode fluxes.

Reproduced with the kind permission of the Australasian Welding Journal

5.17A Weld using gas metal arc welding process (GMAW)

Dangerous fumes

 Dust and vapours are given off in welding

processes, eg: lead, cadmium, zinc.

 Always use ventilation where possible,

otherwise use respirators.

5.17A Weld using gas metal arc welding process (GMAW)

 travels through a solid:

 copper and AL are good conductors

 cast iron and SS are poor conductors they localise heat.

 Radiation:

 travels through air by wave motion:

 no physical contact necessary

 during intensive welding such as pad welding.

Reproduced with the kind permission of Strata Group International

5.17A Weld using gas metal arc welding process (GMAW)

 fills like sand in eyes

 rays very deep penetrating.

 Infra-red:

 like sun burn

 can cause blisters and sores.

 Protect yourself from these by wearing the correct

equipment and lens filters shade 10 minimum.

Reproduced with the kind permission of the Australasian Welding Journal

5.17A Weld using gas metal arc welding process (GMAW)

Hazardous locations

 A hazardous location is an area where flammable or explosive substance are

present or have been.

 No oxygen equipment can be taken into these areas unless a permit is

obtained from a safety officer.

HAZARDOUS LOCATIONS

 Alcohol distilleries, oil refineries, paint factories, explosive plants, coal

crushers, flour mills, saw mills, wheat silos, paper mills.

PROCEDURE FOR HAZARDOUS LOCATIONS

 Inform safety officer of work and equipment to be used.

 Officer must inspect site and make safety recommendations.

 Safety officer must issue a work permit.

 When cutting, welding or heating you must know the location of the

nearest fire brigade and telephone number.

 Have on hand the correct fire extinguishers.

 Wait 1 hour minimum after you have finished cutting, welding or heating.

5.17A Weld using gas metal arc welding process (GMAW)

Confined working areas

Confined working areas are where ventilation or accesses are

restricted.

CONFINED LOCATIONS INCLUDE:

 Tanks, containers, bins, silos, ship hulls, ducts, chutes, pipelines.

PROCEDURES FOR CONFINED SPACES

 Check with supervisor or safety officer before beginning work.

 Ventilate by forced draught (fans).

 Assistant outside at all times.

 Rescue apparatus outside at all times.

 Light blowpipes outside confined spaces.

 Use 32 volt lighting and hand tools.

 Be aware of oxygen enriched atmospheres.

 Be aware of sealed containers (oxygen depleted).

5.17A Weld using gas metal arc welding process (GMAW)

Dangerous containers

 Containers which hold or have held flammables.

 Flammables can get into seams.

 Don’t rely on sight or smell.

 Obtain a chemical analysis.

 Obtain a work permit from a safety officer.

CLEANING AND PURGING PROCEDURES

 Steam clean containers for 30 minutes minimum after

container is hot.

 Fill container with water and bring to a boil Boil for 30

minutes minimum (remove all caps).

 Fill container with water or an inert gas just below weld site

and vent to atmosphere.

 Obtain approval from a safety officer before working on

containers after all of the above.

5.17A Weld using gas metal arc welding process (GMAW)

Welding symbols

 The symbol consists of an arrowhead and leader joined to a

reference line On one or both sides are placed the symbols

with figures that refer to the type of weld and its size.

 A tail may be added for reference notes.

 Basic symbols are used to depict the:

5.17A Weld using gas metal arc welding process (GMAW)

Example - Welding symbol

10mm fillet weld other side.

GMAW

Basic weld symbol.

10 6 6mm fillet weld arrow side.

Weld on site.

Weld all round.

Use the gas metal arc welding process.

5.17A Weld using gas metal arc welding process (GMAW)

Meaning of common symbols

5.17A Weld using gas metal arc welding process (GMAW)

Meaning of common symbols

 12mm fillet weld arrow side of joint:

 bevel preparation arrow side of joint.

 backing bar other side of joint.

 Bevel preparation arrow side of joint:

 flush deposit.

Reproduced with the kind permission of Standards Australia

5.17A Weld using gas metal arc welding process (GMAW)

Meaning of common symbols

 Stitch weld arrow side of joint:

 Staggered stitch weld:

 weld 75mm both sides

 miss 250mm both sides

 125mm between welds centres

either side of joint.

Reproduced with the kind permission of Standards Australia

5.17A Weld using gas metal arc welding process (GMAW)

FLAT OR DOWN HAND

5.17A Weld using gas metal arc welding process (GMAW)

Weld positions

Reproduced with the kind permission of BOC

5.17A Weld using gas metal arc welding process (GMAW)

Weld types

Reproduced with the kind permission of BOC

5.17A Weld using gas metal arc welding process (GMAW)

Fillet weld terms

Heat Effected Zone

Fusion Zone

Weld Metal

Leg Length Reinforcement

Toe

Penetration Parent Metal

5.17A Weld using gas metal arc welding process (GMAW)

Butt weld terms

BUTT WELD TERMS

PARENT METAL

WELD METAL

FUSION ZONE HEAT EFFECTED ZONE

PENETRATION

REINFORCEMENT

INCLUDED ANGLE 60o 70o

THROAT

5.17A Weld using gas metal arc welding process (GMAW)

Butt weld preparations

5.17A Weld using gas metal arc welding process (GMAW)

Butt weld preparations

R5

5.17A Weld using gas metal arc welding process (GMAW)

Methods of plate preparation

 GRINDING

 Grinders are used for fast plate removal.

 By holding the wheel on the edge, fast removal of material is possible.

 Using the flat of the wheel allows for removal of uneven surfaces.

 FLAME CUTTING

 Can be utilised on straight plates or pipes.

 Grinding may be necessary if uneven surfaces

(nicks) are the result of this process.

 MACHINING PREPARATION

 Nibblers are by far the quickest method of removal:

 material thickness from 3 to 40mm possible

 angles of 22o to 45o possible.

 Pipe bevelling machines can be used for preparation of pipes:

 machines are very expensive to purchase.

 Lathe machining can be used:

 time consuming

 plate set up as well as machine set up is required.

Reproduced with the kind permission of BOC

Reproduced with the kind permission of

Trumf

 There are many holding down devices available in the marketplace which

can be purchased to assist in the setting up of the joint and hold it in place whilst tack welding

5.17A Weld using gas metal arc welding process (GMAW)

Material holding devices

Pictures reproduced with the kind permission of Blackwoods &

 Using poor assembly techniques will result in poor quality and also

defective work.

alignment is carried out correctly as per job instruction, welding

procedure or code.

alignment of weld joints.

5.17A Weld using gas metal arc welding process (GMAW)

Material holding devices

Dogs and Wedges Vee block from angle iron

Two pieces of angle iron and a bolt

 During welding, the project may still benefit from the use of holding

down devices to ensure joint alignment throughout welding and

also to minimise the amount of distortion that may occur.

5.17A Weld using gas metal arc welding process (GMAW)

Material holding devices

Reproduced with the kind permission

of Manufacturers Monthly

Strong backs

Positioner & rotator

Element 5.17A.2 Select welding components

In this element you will be required to achieve competency in the following areas:

2.1 Welding machine settings and consumables identified In this

presentation we will look at:

5.17A Weld using gas metal arc welding process (GMAW)

The gas metal arc welding process

wire and the workplace.

from a wire spool into the arc to

form a weld pool.

fully protected from the

atmospheric contamination by a

shielding gas.

by a semi-automatic process by the

operator.

Reproduced by the kind permission of BOC

5.17A Weld using gas metal arc welding process (GMAW)

Gas metal arc welding equipment

Equipment consists of:

 power source transformer/rectifier

 wire feed unit supply constant feed rate

 wire feed rollers correct wire tension

 regulator

 flow meter regulate gas litres / min

 gas cylinder

 shielding gas varies with applications

 contact tip electrical contact

Reproduced by the kind permission of BOC

5.17A Weld using gas metal arc welding process (GMAW)

Power source

 Gas metal arc welding heat is generated by a flow

of current through the gap between the wire

electrode and work piece

 Voltage forms across this gap, which varies with

the arc length.

 A uniform weld is produced by the voltage and the

arc length remaining the same:

 the feed wire is fed into the weld zone at the

same rate at which it melts

or

 melting the feed wire at the same rate it is fed

into the weld zone.

 A constant voltage (potential) power supply has

been developed, because of the need for better arc

control.

 The constant potential (CV) power supply has a

relatively flat volt/ampere characteristic.

 a preset voltage level can be held across its

range.

Reproduced by the kind permission of WIA

The constant potential power supply has

an almost flat voltage/amperage characteristic

Substantial decrease in the current, hence the welding profile changes.

This characteristic is useful when

bridging gaps without stopping

and changing settings, eg: just

increase the stick out length.

Reproduced by the kind permission of BOC

5.17A Weld using gas metal arc welding process (GMAW)

Power source ratings

 A.S 1966 rates electrical power output of welding machines.

 Machines are classified as:

 continuous duty

 heavy duty

 light industrial

 limited output.

 All power sources must display:

 name plate of manufacturer

 equipment class (as above)

 rate output (amperage)

 duty cycle (%).

Reproduced with the kind permission of BOC

5.17A Weld using gas metal arc welding process (GMAW)

Duty cycle

percentage of a five minute period that

the machine will operate at a specified

5.17A Weld using gas metal arc welding process (GMAW)

Wire feed unit

WIRE SPEED

 Wire feed is controlled by the wire feed unit

which is part of the GMAW plant.

 You can increase or decrease the feed rate to

suit particular wire amperages and voltages.

 Because of the constant potential power

source, the welding current output is directly

proportional to wire feed speed.

 Increasing the wire feed will increase the

Reproduced by the kind permission of WIA

stopped.

INCH CONTROL

welding current.

5.17A Weld using gas metal arc welding process (GMAW)

Burn back control

5.17A Weld using gas metal arc welding process (GMAW)

Wire feed roll tension

 Feed units consist of 2 feed rolls (many

combinations now available).

 One roll is grooved to accommodate the

wire diameter and drives the system.

 The other roller is used to apply pressure

to the wire.

 Adjustment is achieved while the wire is

running:

 apply pressure until the roll of wire can

be stopped by slight hand pressure

 too high a pressure will result in

twisting of the wire and flaking

 flaking will clog the wire liner, causing

the wire to jam.

Reproduced by the kind permission of BOC

5.17A Weld using gas metal arc welding process (GMAW)

Wire electrodes

 Wires vary in diameter sizes and are matched to current ranges.

 Chemical composition of wires must be compatible with the

5.17A Weld using gas metal arc welding process (GMAW)

Air and water cooled guns

AIR COOLED GUNS

 Gas metal arc welding produces high heat outputs.

 Guns are designed along with the shielding gases to disperse

the heat output.

WATER COOLED GUNS

 Use higher current densities.

 Water flows through the gun body to cool welding gun unit.

 Water cooled guns are higher in cost.

 They require a constant water supply.

Reproduced by the kind permission of BOC

5.17A Weld using gas metal arc welding process (GMAW)

 correct fit in gas diffuser.

 All of the above will cause faulty welds.

SHROUDS AND GAS DIFFUSERS

 Clean frequently to prevent spatter build up.

 Build up causes bridging or blocked gas flow.

ROLLER SELECTION

 Matching rollers with wire sizes will assure free flow of wires.

 Worn rollers or oversized rollers will decrease wire feed rates.

 Undersized rollers will cause flaking of wire and block liners.

Reproduced by the kind permission of WIA

5.17A Weld using gas metal arc welding process (GMAW)

Cables and liners

resistance to wire feed rates.

(blockages).

Reproduced by the kind permission of WIA

5.17A Weld using gas metal arc welding process (GMAW)

Why use gases

 Shielding gases are important for keeping

the arc stable and protecting the weld

metal from contamination.

 The major function is to surround the

weld zone with a non-reactive shielding

5.17A Weld using gas metal arc welding process (GMAW)

Typical shielding gases

Reproduced by the kind permission of BOC